U.S. Pat. No. 7,882,824 B2 discloses a method for recovering vapor during an onboard refueling operation comprising the steps of: providing a flow path between a fuel tank and a purge canister; providing a valve in the flow path; providing a fuel level sensor for indicating the level of fuel in the fuel tank, and a vapor pressure sensor for indicating the pressure of the fuel vapor in the fuel tank; and actuating the valve to selectively open and close the flow path in response to signals received from the fuel level sensor and the vapor pressure sensor.
It is a disadvantage of the prior art that the point at which the valve is closed after the detection of the nozzle shut-off is not defined and can be chosen arbitrarily. If the valve closing is done at a too high remaining internal tank pressure, the risk of spill-over increases. If the valve closing is done at a too low remaining pressure, the operator can still add some fuel and thus the venting function can be degraded.